The invention relates to gasification of solid carbonaceous fuels such as coke, coal, or lignite. More specifically, the invention relates to a system for detecting the level of slag that can accumulate in the quench section of a solid fuels gasification reactor.
Solid fuels, such as coal, coke, or lignite can be used to make a useful synthetic gas product. In a typical process for gasifying coal, the solid lumps are ground into fine particles, mixed with oil or water, and fed into a gasification reactor. During the gasification process a substantial amount of molten slag forms in the hearth section of the reactor. The fluid slag then flows out of the hearth section through a taphole and down through a diptube into a quench chamber below the hearth. From the quench chamber, the slag drops down into a crusher unit that breaks it up and discharges it from the bottom of the reactor in a slurry form.
It is desirable to keep the temperature in the hearth as low as possible, to increase the life of the refractory lining and to improve gasification efficiency. The minimum operating temperature is usually determined by the melt temperature of the slag, since the slag has to flow through the taphole. But, if the reactor is running too close to the slag fluid temperature, the slag often forms long clinkers as it flows out of the taphole into the quench chamber. These clinkers tend to "bridge over" the inlet to the crusher unit, so that eventually the quench chamber and diptube fill up and the taphole is plugged off.
When the taphole becomes plugged, the reactor has to be shut down and the slag clinkers removed, which is a time-consuming procedure. Although there are "on-line" procedures for clearing the slag bridges in the quench chamber, such procedures are not entirely satisfactory. For example, the measures presently in use are detrimental to product gas quality, they're too costly, and they can damage the refractory lining in the taphole. Another major drawback is that the reactor operator has no clear indication of when the removal procedure needs to be initiated, because the slag build up forms under the surface of the water in the quench chamber. Inside this chamber the water is black, very hot and turbulent, and the pressure can be as high as 500 psi.